Ball and socket joints, as they are used especially for wheel suspensions in motor vehicles, are at times subject to extreme loads, which may consist of mechanical stresses or are caused by thermal or chemical effects. They are currently designed such that they do not have to be replaced and do not require maintenance under normal circumstances during the service life of a motor vehicle.
Ball and socket joints are subject in motor vehicles to radial and axial forces, which may at times assume considerably high values. In addition, the ball pivot must make possible a rotary motion about its central axis. The torques and moments of friction that can be observed in the ball and socket joint also increase with increasing size of a ball and socket joint. This has an adverse effect especially in the area of the steering, because increased forces are to be applied here in order to guarantee steerability of the motor vehicle. Moreover, high torques and moments of friction within the ball and socket joint lead to wear as well as to the risk that specifications mandated by law concerning the steering return cannot be met.
To reduce the torques and moments of friction within a ball and socket joint, for example, the ball and socket joints known from U.S. Pat. No. 2,954,993 and U.S. Pat. No. 2,645,510 have a ball pivot, which is equipped with a spheroidal bearing surface mounted pivotably and rotatably in a housing, wherein a roller bearing is present between the first spheroidal bearing surface and another spheroidal bearing surface, which is mounted in the housing and is connected to the ball pivot. Single-row deep groove ball bearings are used as roller bearings according to the disclosure contents of said documents. The joint ball comprises in these solutions two separate individual parts each, said roller bearing being accommodated between the parts of the joint ball. As a consequence of the low rolling friction of the roller bearings, a rotary motion of the ball pivot can be converted with such a ball and socket joint with very low moments of friction.
However, the ball and socket joints known from said documents also have drawbacks. For example, there are metallic, spheroidal bearing surfaces, which are mounted directly in a housing likewise consisting of a metal. Due to the metal-on-metal contact pairing, vibrations introduced from the road surface via the wheel suspension and the ball and socket joint located therein are passed on to the components of the motor vehicle accommodating the ball and socket joint directly, i.e., without absorption, and they can therefore be felt by the driver of the vehicle. However, this is associated with a reduction of comfort, which is not acceptable. It is, moreover, necessary as a consequence of the bearing pairing used to perform maintenance on the ball and socket joints at regular intervals. Maintenance consists in this case of the need to refill grease via lubricant filling openings present on the ball and socket joint.
However, the essential drawback of the ball and socket joint designs known from U.S. Pat. No. 2,954,993 and U.S. Pat. No. 2,645,510 can be seen in the fact that the roller bearings used are designed exclusively for loading in the axial direction relative to the non-deflected ball pivot. The roller bearings used here are not suitable for absorbing and passing on radial forces.
Moreover, the problem arises in such roller bearings that the clearance also increases with the roller bearing when wear develops on the joint and an associated loosening of the inner components of the joint occurs. However, it can happen as a result that the rollers will be displaced and jammed and their trouble-free operation is thus not guaranteed any longer. The consequence inevitably arising from this for the ball and socket joint in question would be that the ball and socket joint would have to be replaced as a whole.
Another solution appears from U.S. Pat. No. 2,544,583. The ball and socket joint described there is designed for wheel suspensions in motor vehicles. It has a ball pivot, which is equipped with a first spheroidal bearing surface mounted pivotably and rotatably in a housing, wherein a roller bearing is present between the first spheroidal bearing surface and another spheroidal bearing surface, which is mounted in the housing and is connected to the ball pivot. The roller bearing described in this document is a cylindrical roller bearing. Such cylindrical roller bearings are suitable for absorbing strong radial forces relative to the axis of rotation of the rollers. However, cylindrical roller bearings can transmit only extremely weak axial forces at best. Such a ball and socket joint can have very limited use only in case of the complex loads to which a ball and socket joint is subject in a motor vehicle, which also involve superimposed force and torque effects in the axial as well as radial directions. The embodiment described in this document is also a metal-on-metal bearing, because both the parts of the joint ball and the housing are manufactured from a metallic material and form a direct contact pair. The joint according to U.S. Pat. No. 2,544,583 therefore also requires permanent maintenance at fixed time intervals, which is carried out by greasing, as in the ball and socket joints described before, which are known from the state of the art. The ball and socket joint described in U.S. Pat. No. 2,544,583 also has a lubricant filling opening for this purpose.